As one of the control systems for the network system, a CU (C: control plane/U: user plane) separation type network system is proposed in which a node apparatus (user plane) is controlled from an external control unit (control plane).
As an example of the CU separation type network system, an open flow network system using the open flow (Openflow) technique is known which controls switches from a controller to carry out a route control of the network. The details of the open flow technique have been described in Non-Patent Literature 1. It should be noted that the opening flow network system is an example only.
(Explanation of Open Flow Network System)
In the open flow network system, a controller such as an OFC (Openflow Controller) controls the conducts of the switches by operating flow tables of switches such as OFSs (Openflow switches). The controller and the switch are connected with a secure channel.
The switch in the open flow network system forms an open flow network and is an edge switch or a core switch, which is under the control of the controller. A series of processing to the packet from the reception (inflow) of the packet in the edge switch on the input side to the transmission (outflow) from the edge switch on the output side in the open flow network is called a flow.
The packet may be read as a frame. The packet and the frame are different only in data unit of protocol (PDU: Protocol Data Unit). The packet is a PDU of “TCP/IP” (Transmission Control Protocol/Internet Protocol). On the other hand, the frame is a PDU of the “Ethernet (registered trademark)”.
The flow table is a table in which a flow entry is registered to define a predetermined operation (action) to be carried out to the packet (communication data) which matches a predetermined match condition (rule). That is, the flow table stores a set of the flow entries.
The rule of the flow entry is defined based on various combinations of all or part of a destination address, a source address, a destination port, and source port, which are contained in the header field of the packet for each protocol hierarchical layer, and is identifiable. It should be noted that it is supposed that the above-mentioned address contains a MAC address (Media Access Control Address) and IP address (Internet Protocol Address). Also, data in the input port (Ingress Port) in addition to the above data is usable for the rule of the flow entry. Also, as the rule of the flow entry, the one which has expressed a part (or all) of a value of the header field of the packet which shows a flow can be set in the formation of a normal expression and wildcard “*” and so on.
The action of the flow entry is an operation such as “output to specific port”, “discard”, and “rewrite a header”. For example, if identification data of the output port (output port number and so on) is shown in the action of the flow entry, the switch outputs the packet to the port corresponding to this. The packet is discarded if the identification data of the output port is not shown. Or, the switch rewrites the header of the packet based on header data if the header data is shown in the action of the flow entry.
The switch in the open flow network system executes the action of the flow entry to the packet group (packets) which match the rule of the flow entry.
(Multicast Transmission in Existing Open Flow Network System)
In the open flow network system, the multicast transmission of the packet is sometimes carried out as in the conventional network system.
The multicast transmission is a technique for transmitting the packet to a plurality of destinations by specifying one destination. By using the multicast transmission, the same data can be transmitted to a plurality of users in the network.
To realize the processing for the multicast transmission by the switch of the open flow network system, the header of the received packet is rewritten and the received packet must be outputted to each destination port.
However, because the switch can execute the conversion action of the packet only once, when multicast transmission can be carried out in the switch, there are constraints that it is possible to transmit to a single VLAN (virtual LAN) but it is not possible to transmit to a plurality of VLANs which are different from each other.